Method for manufacturing an armature for an electric motor

ABSTRACT

An armature for an electric motor with a shaft, a stack of laminations arranged on the shaft, a commutator likewise arranged on the shaft and comprising several commutator segments and a plastic filling, and a wire winding wound around the stack of laminations and welded to the commutator is manufactured by first fixedly arranging a commutator blank without plastic filling by means of an auxiliary assembly device on the shaft, then attaching and welding the wire winding to the commutator blank, subsequently filling the assembly consisting of commutator blank, stack of laminations and wire winding with plastic and uniting it into an inherently stable, compact unit, and, finally, removing the auxiliary device again.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for manufacturing an armature for anelectric motor with a shaft, a stack of laminations arranged on theshaft, a commutator likewise arranged on the shaft and comprisingseveral commutator segments and a plastic filling, and a wire windingwound around the stack of laminations and welded to the commutator.

2. The Prior Art

In the methods hitherto generally performed for manufacturing sucharmatures, prefabricated components are used, in particular, aprefabricated commutator, and the commutator comprises the usual ringconsisting of copper segments insulated from one another and a plasticfilling introduced into the interior of the ring and usually consistingof thermosetting plastic, with a central bore. The stack of laminationsand the commutator are pushed with a tight fit onto the shaft, and thestack of laminations can be additionally supported at the end facesthereof. The wire winding consisting of insulated copper wire is thenplaced around the stack of laminations so as to extend in the groovesthereof and is connected by welding to the individual segments of thecommutator so that all of the commutator segments are provided withwires and the wire winding comprises a previously determined number ofwindings. During the joining of the copper wire to the commutatorsegments, such heat is generated that the enamel insulation of thecopper wire burns off, and the wire may start to glow. Finally, acasting lacquer is introduced in drops into and cured in the area of thewire winding between commutator and stack of laminations so that theindividual wires of the wire winding are fixed in relation to oneanother.

The armatures for electric motors manufactured in accordance with thehitherto method have two main disadvantages: The prefabricatedcommutator is fixed on the armature shaft by being pushed with its innerplastic filling with a press fit onto the shaft. Since the shaftdiameter for achieving the press fit is somewhat larger than the bore inthe plastic filling of the commutator, the commutator is necessarilywidened somewhat, in all, which can cause loosening of the firm seatingof the commutator segments in the plastic filling and impairment of therunning characteristics of the electric motor. As long as the plasticfilling of the commutators consisted of thermosetting plastics filledwith asbestos, the filling had an excellent elasticity and a very strongadhesion to the copper metal of the commutator and so the aforementioneddisadvantage virtually did not occur. However, such thermosettingplastics filled with asbestos are now no longer allowed to be used inview of their detrimental effect on health.

The further main disadvantage of the armatures manufactured inaccordance with the above method originates from the welding of thewires to the commutator segments, which is carried out under the actionof strong heat. The welding temperatures must be so high that theinsulating enamel of the copper wire burns. This results in temperaturesoccurring at least for a short time at the commutator, which are higherthan those tolerated by the thermosetting plastics forming the plasticfilling. The welding thus results in a certain damage in advance to thecommutator. As long as the commutators comprised thermosetting plasticscontaining asbestos, the high welding temperature was unproblematicbecause these thermosetting plastics were insensitive to heat to thatextent. However, damage to the asbestos-free plastic filling of thecommutator owing to the high welding temperatures now likewise resultsin a considerable reduction in the service life of the electric motorarmature.

SUMMARY OF THE INVENTION

Therefore, the object of the invention is primarily to propose a newmethod for manufacturing armatures for electric motors with a stack oflaminations which is free from the deficiencies explained hereinaboveand results in a firm seating of the commutator on the armature shaft,but not in damage to the commutator in the course of the welding of thewire winding, in particular, also when the commutator has anasbestos-free plastic filling.

The object is accomplished in accordance with the invention by

a) first fixedly arranging a commutator blank without plastic filling bymeans of an auxiliary assembly device on a shaft, then

b) attaching the wire winding and welding it to the commutator blank,subsequently

c) enclosing the assembly consisting of commutator blank, stack oflaminations, wire winding and auxiliary assembly device with a mold,with the auxiliary assembly device forming part of this mold andcodetermining the outer shape of the plastic filling, then

d) filling the assembly consisting of commutator blank, stack oflaminations, wire winding and auxiliary assembly device in the mold withplastic and uniting it into an inherently stable, compact unit, and,finally,

e) after removal of the assembly from the mold, removing the auxiliarydevice again, and making the commutator blank into the final commutator.

From U.S. Pat. No. 3,212,170 it is known to mold the armature of anelectric motor with plastic after its winding has been soldered to thecommutator. However, this relates to armatures without a stack oflaminations, which can only be employed for special electric motors. Anauxiliary assembly device, as provided in accordance with the invention,which not only serves to perform the assembly operation of thecommutator, but also functions as part of the mold, is missing in theaforementioned publication.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of preferred embodiments of the inventionserves in conjunction with the appended drawings to explain theinvention in further detail. The drawings show:

FIG. 1 a sectional view of an armature for an electric motor at acertain manufacturing stage taken along line 1--1 in FIG. 2;

FIG. 2 a sectional view taken along line 2--2 in FIG. 1;

FIG. 3 a view of the armature from FIG. 1 at a subsequent manufacturingstage after a wire winding has been partly wound on;

FIG. 4 the armature from FIG. 3 in a casting or injection mold;

FIG. 5 the mold from FIG. 4 filled with plastic;

FIG. 6 the armature removed from the mold according to FIG. 5;

FIG. 7 the armature from FIG. 6 after slots have been sawn in acommutator blank;

FIG. 8 a sectional view of another embodiment of an armature for anelectric motor taken along line 8--8 in FIG. 9;

FIG. 9 a sectional view taken along line 9--9 in FIG. 8;

FIG. 10 the armature from FIG. 8 in a mold;

FIG. 11 the armature from FIG. 10 after an auxiliary shaft has beenexchanged for a final armature shaft;

FIG. 12 a sectional view of a further embodiment of an armature for anelectric motor with an auxiliary shaft;

FIG. 13 the armature from FIG. 12 cast with a plastic filling after theauxiliary shaft has been exchanged for the final armature shaft; and

FIG. 14 a further embodiment of an armature for an electric motor withdouble insulation in the area of the commutator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The main steps of the inventive method for manufacturing an armature foran electric motor are described hereinbelow with reference to FIGS. 1 to7.

As shown in FIG. 1, a stack of laminations 2 is pushed in the usual waywith a tight fit onto a shaft 1 of an armature for an electric motor.The first and last laminations of the stack of laminations areadditionally supported by hat-shaped sleeves 3 and 4, respectively, atthe end faces of the stack of laminations 2. A commutator blank 5 in theform of a continuous ring made of copper is inserted with a tight fitinto a corresponding cylindrical recess 6 of an auxiliary assemblydevice 7. The auxiliary device 7 has the shape of a cylindrical assemblybush and comprises a relatively thick bottom part 8 with a central bore9, with which the auxiliary device 7 is pushed with a tight fit onto theend of the shaft 1. The ring-shaped commutator blank 5 is thereby firmlysupported at the side of the stack of laminations 2 in a cantilevermanner over the shaft 1, and, in particular, a relatively large spaceremains free between the inner side of the commutator blank 5 and theouter side of the shaft 1.

Integrally formed on the ring-shaped commutator blank 5 are small feet11 of T-shaped cross section which are oriented radially inwardly andare mutually spaced from one another. Likewise integrally formed on thecommutator blank 5 on the side thereof facing the stack of laminations 2are hooks 12 which are mutually spaced from one another.

Several channels 13 provided on the auxiliary assembly device 7 extendcontinuously in the axial direction from the free end face of theauxiliary device 7 into the free space inside the commutator blank 5.

FIG. 3 shows a manufacturing stage of the armature at which a wirewinding 14 is partially wound onto the stack of laminations 2. On theone hand, the wire winding extends in grooves 15, which are usuallyprovided in the stack of laminations 2, and, on the other hand, it iswelded with its ends in a likewise conventional manner to the hooks 12of the commutator blank 5. During the welding operation, the commutatorblank 5 is held firmly on the shaft 1 by the auxiliary device 7. Sincethe commutator blank is not filled with plastic, it cannot be damaged bythe action of the heat occurring during the welding. In the course ofthe welding, the wire forming the wire winding 14 is heated in the areaof the hooks to the extent that an enamel insulation located on thewire--usually copper wire--melts, and an electrically conductiveconnection is established between the hooks 12 and the wire.

After completion of the wire winding 14, the hooks 12 are bent towardsthe commutator blank 5--possibly simultaneously with the welding--in theway shown in FIG. 4. The unit consisting of shaft 1, stack oflaminations 2, commutator blank 5, auxiliary assembly device 7 and wirewinding 14 is then placed in a mold 18 consisting of two halves 16, 17,as shown in FIG. 4. The one end wall of the auxiliary assembly device 7(on the left in FIG. 4) forms part of the mold 18 by closing off itscavity towards the one side. The unit described hereinabove is heldsecurely in the cavity of the mold 18, on the one hand, (on the left inFIG. 4) by the shaft 1 and, on the other hand, (on the right in FIG. 4)by the auxiliary device 7.

A plastic filling is now introduced, in particular, by injectionmolding, transfer molding or compression molding, through the channels13 of the auxiliary assembly device 7 into the cavity of the mold 18.The thus introduced plastic fills out all of the free spaces of the mold18, in particular, the space inside the commutator blank 5, and alsoencloses the wire winding 14 including the hooks 12 on the commutatorblank 5, as shown in FIG. 5, in which the plastic filling is denoted byreference numeral 19. The small feet 11 serve to anchor the commutatorblank 5 firmly in the plastic.

FIG. 6 shows the armature 21 released from the mold 18 and cast withplastic, after the auxiliary assembly device 7 has been subsequentlyremoved from the commutator blank 5, so the surface of the latter is nowfreely exposed.

FIG. 7 shows the armature 21 in its final stage of manufacture whichdiffers from the stage of manufacture according to FIG. 6 in thataxially parallel slots 20 have now been sawn in the area of thecommutator blank 5 between the individual hooks 12 covered by plastic.These slots extend through the entire blank as far as its inner plasticfilling, thereby producing individual commutator segments 22 which areelectrically separated from one another. Each one of these commutatorsegments is connected in the conventional manner by the hook 12integrally arranged on it to a corresponding part of the wire winding14. The slots 20 are sawn over the entire axial extent of the commutatorblank 5, i.e., starting each time from the edge carrying the hooks 12 tothe opposite edge.

As shown in FIG. 7, on this opposite edge of the commutator blank 5, inthe area of the slots to be sawn, "windows" 23, in which the slotterminates, are formed on both sides. Such windows 23 can also be formedbetween the hooks 12 on the opposite edge of the commutator blank. Thesawing is carried out with the aid of a small circular saw, with the cutstarting at the edge of the commutator blank 5 carrying the hooks 12 andterminating in the windows 23 at the opposite edge. The windows filledwith plastic prevent the saw blade from forming a burr on the individualcommutator segments when it exits, and so the danger of a electricalshort circuit is eliminated.

The final commutator 25 is thus produced from the original commutatorblank 5.

The finished commutator 25 is firmly anchored on the shaft 1 by theplastic subsequently pressed into the interior of the commutator blank5. The hitherto existing danger of expansion of the commutator when thecommutator previously filled with plastic is subsequently pressed ontothe shaft 1 is eliminated. Since the welding of the wire winding 14 tothe hooks 12 of the commutator blank 5 is also carried out prior tointroduction of the plastic filling 19, the latter is in no way damagedby the heat occurring during the welding, and, therefore, the servicelife of an electric motor equipped with an armature made in the mannerdescribed hereinabove is not shortened. Since the plastic filling 19 isnot subjected to the action of heat in the course of the manufacture ofthe armature 21, other plastics than those hitherto used can also beemployed, for example, also thermoplastics.

FIGS. 8 to 11 serve to explain a further embodiment of the invention. Incontrast to the embodiment according to FIGS. 1 to 7, in the embodimentaccording to FIGS. 8 to 11 the commutator blank 5 does not consist of aring closed within itself and made, for example, from a band of sheetcopper, but, from the start, of individual commutator segments 26 withhooks 27, windows 28 and small, radially inwardly projecting feet 29. Anauxiliary shaft 31 with a thicker cylindrical section 32 is used to holdthese individual commutator segments such that they lie in contiguousrelation to one another in a circle. The small feet 29 of the commutatorsegments 26 are supported on the outside of the thicker shaft section 32and are held together on the outside by a solid ring 33 made of metal.This results in a commutator blank 5 which corresponds substantially tothe commutator blank 5 according to FIGS. 1 and 2, with the exceptionthat it is not of "cantilever" design, but is held together similarly toan arch by the thicker shaft section 32 located on the inside and theouter ring 33. The individual commutator segments 26 lie with their sidewalls in immediately adjacent relation to one another, i.e., inelectrically conductive contact with one another.

The stack of laminations 2 and the sleeves 3, 4 are also fitted on theshaft 31 in the manner described hereinabove (cf. FIG. 1). As shown inFIG. 10, the assembly is then placed in a mold 18, in accordance withFIG. 4, with the ring 33 now serving to hold the assembly in the mold18. Before the assembly was placed in the mold 18, the wire winding 14was attached and welded to the hooks 27 in the manner likewise describedhereinabove, and the hooks were then bent, as shown in FIG. 10. Theauxiliary shaft 31 is then pulled out and replaced by the actual orfinal armature shaft 1 (FIG. 11). As shown, the commutator blank 5comprised of the individual commutator segments 26 is held in the mold18 in a cantilever manner via the ring 33 and forms a free space towardsthe shaft 1. A cover 34 with channels 35 is now placed tightly on themold 18 and plastic is pressed in so as to fill the entire free spacesin the mold 18, in particular, the ring-shaped space between shaft 1 andcommutator blank 5. After the plastic has cured, the armature filledwith and enveloped by plastic is removed from the mold 18. After removalof the ring 33, sawing is then carried out continuously between theindividual commutator segments 26 as far as the plastic filling in themanner likewise described hereinabove so as to produce commutatorsegments which are electrically insulated from one another. These areheld together by the plastic filling and are each connected to acorresponding part of the wire winding 14 via the hooks 27. The finalproduct obtained after completion of the method in accordance with FIGS.8 to 11 corresponds virtually to the product shown in FIG. 7.

It is to be noted that in the methods described hereinabove, the grooves15 of the stacks of laminations which receive the wire winding 14,possibly with insulating strips of paper placed therebetween, are alsofilled with plastic, as indicated in FIG. 5, when the plastic isintroduced.

In the embodiments of electric motor armatures according to FIGS. 12 and13, a ring-shaped commutator blank 5 closed within itself is again used.It is held in an auxiliary assembly device 7 in the form of acylindrical assembly bush.

In other respects, FIG. 12 corresponds substantially to FIG. 1. However,in contrast to FIG. 1, in FIG. 12 it is not the final armature shaft 1but an auxiliary shaft 36 that is used. After formation of the wirewinding 14 and connection thereof to the hooks 12 of the commutatorblank 5 (not shown in FIGS. 12 and 13), the thus prepared armature isinserted with the auxiliary shaft 36 into a mold 18 (similar to FIG. 4).The auxiliary shaft 36 is now pulled out (towards the right) andreplaced by the actual armature shaft 1 (FIG. 13) which has a smallerdiameter than the auxiliary shaft 36. This produces in the mold betweenthe shaft 1 and the inner sides of the stack of laminations 2 and alsothe sleeves 3, 4 a ring-shaped space which is likewise filled withplastic and so an electrically insulating plastic tube 37 is formedbetween the stack of laminations 2 and the shaft 1. Electricallyinsulated armatures such as are prescribed for certain electricapparatus can be manufactured in this way.

Furthermore, as is shown in FIG. 13, the shaft 1 has knurled portions 38for better adhesion of the plastic to the shaft.

Finally, FIG. 14 shows a further modified embodiment of an armature foran electric motor, which was manufactured in accordance with the methoddescribed hereinabove and is "double insulated" due to a relativelyshort tube 39 made of electrically insulating material being arrangedbetween the plastic filling 19 in the area of the commutator blank 5 andthe shaft 1. This tube 39 is mounted before the plastic filling 19 isinjected into the mold 18.

In another embodiment of the invention similar to that which wasdescribed in conjunction with FIGS. 8 to 11, electrically insulatinglayers made, for example, of micanite, are inserted between theindividual commutator segments 26 of the commutator blank 5. In thiscase, the subsequent sawing of the slots between the commutator segments26 is dispensed with, since these are electrically insulated from oneanother from the start.

On the other hand, from the start, individual commutator segments ofwhich the commutator blank 5 is made up can be held centrally inrelation to the armature shaft 1 at mutual spacings in the mold by acorrespondingly adapted auxiliary device 7 such that the plastic flowsin between the individual segments and insulates these electrically fromone another. In this case, too, the subsequent sawing of slots can bedispensed with.

In the course of the finishing, the armature also has to be balanced.This can be carried out advantageously in the following way: Afterremoval from the mold and prior to turning of the brush track of thecommutator, the armature around which plastic has been injected isclamped on the outside of the stack of laminations, and bearing seatsare then ground or turned at the ends of the shaft 1. The balancing isthen carried out in the manner known per se. It is, however, to beexpected that the correction to be made during this operation will berelatively small. After measuring the balance error and after turningthe brush track of the commutator, a further possibility consists in soadjusting two cutter or grinding heads placed at the ends of thearmature shaft 1 eccentrically in their center axial position inrelation to the center axis of the armature shaft 1 and then somachining the bearing seats at the shaft ends that the balance error isthereby compensated.

In the embodiments of the invention described hereinabove, the wirewinding 14 is connected to hooks 12 or 27 of the commutator. Instead ofsuch hooks, it is also possible to use slots in the commutator blankinto which the wire ends of the wire winding are welded.

As described hereinabove and illustrated, plastic can be molded over thehooks 12, 27 on the commutator to the extent that a sufficiently widebrush track remains on the commutator itself. This brush track isdenoted by reference numeral 41 in FIG. 14, but, in reality, it can bemade wider by the plastic coating covering the hooks 12 extending lessfar over the commutator 25.

For improved fixing of the commutator 25 on the armature shaft 1, it isalso possible to provide knurls or splints--similar to the knurls 38 inFIGS. 13 and 14--in the area of the commutator for providing goodadhesion to the injected plastic.

As described hereinabove, with commutators 25 which from the startconsist of individual, mutually insulated commutator segments 26, i.e.,do not have to be sawn, it may prove expedient to stabilize thesesegments on the outside by plastic rings injected onto them. On the onehand, such stabilization is already effected by injecting plastic overthe hooks 27 connected to the wire winding 14 (FIG. 11). On the otherhand, as explained hereinbelow with reference to FIG. 1, shoulder-likerecesses 42 in the form of steps can be provided at the edges of theindividual segments 26 facing away from the hooks 12. During theinjection molding, these likewise become filled with plastic and form aring which stabilizes the individual segments 26.

We claim:
 1. A method for manufacturing an armature for an electricmotor comprising the steps of:a) securing a commutator blank to anauxiliary assembly device and mounting the auxiliary assembly deviceonto a shaft; b) winding wire conductors onto a stack of laminationspositioned on the shaft and welding the wire conductors to thecommutator blank; c) enclosing the conductors, laminations, andcommutator blank within a mold in which the auxiliary assembly devicedefines a section of the mold wall; d) filling the mold with plastic toform a rigid assembly; e) withdrawing the rigid assembly from the mold;f) removing the auxiliary assembly device from the shaft; and g)dividing the commutator blank into a plurality of commutator segments.2. The method of claim 1, wherein the auxiliary assembly devicecomprisesa cylindrical receptacle secured to an outer surface of thecommutator blank, and a bore frictionally receiving the shaft.
 3. Themethod of claim 1, wherein said step (d) of filling comprises injectionmolding plastic into the mold.
 4. The method of claim 1, wherein saidstep (d) of filling comprises transfer molding plastic into the mold. 5.The method of claim 1, wherein said step (d) of filling comprisescompression molding plastic into the mold.
 6. The method of claim 1,wherein the commutator blank comprisesa first end and an opposite secondend, and a plurality of slots formed in at least one end which aresubsequently filled with plastic.
 7. The method of claim 1, wherein thewelds between the wire conductors and the commutator blank are encasedin plastic.
 8. The method of claim 1, wherein said step (g) of dividingcomprises cutting a plurality of parallel insulating slots into thecommutator blank.
 9. The method of claim 1, wherein the stack oflaminations includes grooves which receive the wire conductors and areencased by plastic.
 10. The method of claim 1, wherein the shaftincludes spaced apart ends having bearing surfaces.
 11. The method ofclaim 1, wherein the shaft in step (a) comprises an auxiliary shaftwhich is exchanged for an armature shaft prior to said step (d) offilling.
 12. The method of claim 11, wherein the auxiliary shaft has alarger diameter than the armature shaft, the difference in diameterbeing occupied by plastic thereby forming additional insulation betweenthe armature shaft and the stack of laminations.
 13. The method of claim1, wherein the commutator blank comprisesa first end to which the wireconductors are welded, and a second opposite end including slots whichare filled with plastic.
 14. The method of claim 1, wherein the mold isfilled with plastic through a sprue formed within the auxiliary assemblydevice.
 15. A method for manufacturing an armature for an electric motorcomprising the steps of:a) securing a plurality of commutator segmentsto an auxiliary shaft by encircling the segments with an auxiliaryassembly device; b) winding wire conductors onto a stack of laminationspositioned on the auxiliary shaft and welding the wire conductors to thecommutator segments; c) enclosing the conductors, laminations, andcommutator segments within a mold in which the auxiliary assembly devicedefines a section of the mold wall; d) replacing the auxiliary shaftwith an armature shaft; e) filling the mold with plastic to form a rigidassembly; f) withdrawing the rigid assembly from the mold; and g)removing the auxiliary assembly device from the commutator segments. 16.The method of claim 15, wherein the secured commutator segments areelectrically insulated from each other.